The present invention pertains to a novel core drilling tool system which allows for less mechanically stressed axial settings and adjustments in the inner unit of a core barrel.
In a known core drilling tool, as described in U.S. Pat. No. 4,300,643, the conical setting threads of the setting device also form the connector threads for supporting the inner unit in the outer housing. A tubular shoulder of the inner unit, including an axial lock groove at its outside into which locking pawls can be inserted from above by a cylindrical locking element, protrudes upward into a region over the setting threads. The pawls also protrude over the lower edge of the locking part and can be fit into slits in a lower shoulder of an expanded inner hole of the outer housing. To make an adjustment, one has to screw the outer housing onto a separation point located near the adjuster, insert a key from above into the lower tool section and mesh it with the inner unit, lift the lock, and then twist and axially adjust the inner unit.
Adjustments to this design require a large torque on the key because the complete weight of the inner element rests on the thread area of the adjuster threads. This practically eliminates any adjustment of heavy inner units, e.g. those with long inner tubes. In addition, the adjusting device is covered during adjustments and cannot be checked visually for proper operation.
This problem also applies to another known core drilling tool, as disclosed in European Patent No. 0174 615, where the shoulder of the inner element protrudes over the common setting and connecting threaded joint between the inner element and the outer housing. The shoulder is slit and thus provides spreader tongues with outer locking pawls which mesh with axial locking grooves disposed on the inside of the outer housing when a spreader element is screwed in.